/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.hash;

import com.google.caliper.BeforeExperiment;
import com.google.caliper.Benchmark;
import com.google.caliper.Param;

import java.util.Random;
import java.util.zip.Adler32;
import java.util.zip.CRC32;
import java.util.zip.Checksum;

/**
 * Benchmarks for comparing {@link Checksum}s and {@link HashFunction}s that wrap {@link Checksum}s.
 *
 * <p>Parameters for the benchmark are:
 *
 * <ul>
 *   <li>size: The length of the byte array to hash.
 * </ul>
 *
 * @author Colin Decker
 */
public class ChecksumBenchmark
{

    // Use a constant seed for all of the benchmarks to ensure apples to apples comparisons.
    private static final int RANDOM_SEED = new Random().nextInt();

    @Param({"10", "1000", "100000", "1000000"})
    private int size;

    private byte[] testBytes;

    @BeforeExperiment
    void setUp()
    {
        testBytes = new byte[size];
        new Random(RANDOM_SEED).nextBytes(testBytes);
    }

    // CRC32

    @Benchmark
    byte crc32HashFunction(int reps)
    {
        return runHashFunction(reps, Hashing.crc32());
    }

    @Benchmark
    byte crc32Checksum(int reps) throws Exception
    {
        byte result = 0x01;
        for (int i = 0; i < reps; i++)
        {
            CRC32 checksum = new CRC32();
            checksum.update(testBytes);
            result = (byte) (result ^ checksum.getValue());
        }
        return result;
    }

    // Adler32

    @Benchmark
    byte adler32HashFunction(int reps)
    {
        return runHashFunction(reps, Hashing.adler32());
    }

    @Benchmark
    byte adler32Checksum(int reps) throws Exception
    {
        byte result = 0x01;
        for (int i = 0; i < reps; i++)
        {
            Adler32 checksum = new Adler32();
            checksum.update(testBytes);
            result = (byte) (result ^ checksum.getValue());
        }
        return result;
    }

    // Helpers + main

    private byte runHashFunction(int reps, HashFunction hashFunction)
    {
        byte result = 0x01;
        // Trick the JVM to prevent it from using the hash function non-polymorphically
        result ^= Hashing.crc32().hashInt(reps).asBytes()[0];
        result ^= Hashing.adler32().hashInt(reps).asBytes()[0];
        for (int i = 0; i < reps; i++)
        {
            result ^= hashFunction.hashBytes(testBytes).asBytes()[0];
        }
        return result;
    }
}
